A CMOS low-voltage low-power temperature sensor

Temperature sensing circuits are used in a wide range of applications such as in the biomedical area, cold chain monitoring and industrial applications. In the biomedical area, temperature patient monitoring systems can be found in a wide range of hospital applications such as the intensive care unit, surgery rooms and clinical analysis. When the systems also incorporate also communication features, they form a telemedicine system in which the patients can be remotely monitored. The need of portability promotes a demand for sensors and signal conditioners that can be placed directly on the patient or even implanted. Implanted systems provide comfort for the patient during the physiologic data acquisition. These systems should operate preferably without a battery, in which the energy is obtained by inductive coupling (RF link). Implanted devices require low-voltage and low-power operation in a small silicon area in order to offer safety to the patient, mainly in terms of excessive exposure to RF. This work presents a low-voltage low-power temperature sensor, suitable for implanted devices. The circuit topology is based on the composite transistors operating in weak inversion, requiring extremely low current, at low-voltage (0.8 V), with just 100 nW power dissipation. The circuit is very simple and its implementation requires a small silicon area (0.062 mm2). The tests conducted in the prototypes validate the circuit operation.